Replace floating point arithmetic with integer arithmetic (#5181)

4 files changed, 10 insertions, 15 deletions

diff --git a/src/cryptography/hazmat/backends/openssl/rsa.py b/src/cryptography/hazmat/backends/openssl/rsa.py
index 3e4c2fd2..458071ca 100644
--- a/src/cryptography/hazmat/backends/openssl/rsa.py
+++ b/src/cryptography/hazmat/backends/openssl/rsa.py
@@ -4,8 +4,6 @@
 
 from __future__ import absolute_import, division, print_function
 
-import math
-
 from cryptography import utils
 from cryptography.exceptions import (
     InvalidSignature, UnsupportedAlgorithm, _Reasons
@@ -352,7 +350,7 @@ class _RSAPrivateKey(object):
         return _RSASignatureContext(self._backend, self, padding, algorithm)
 
     def decrypt(self, ciphertext, padding):
-        key_size_bytes = int(math.ceil(self.key_size / 8.0))
+        key_size_bytes = (self.key_size + 7) // 8
         if key_size_bytes != len(ciphertext):
             raise ValueError("Ciphertext length must be equal to key size.")
 
diff --git a/src/cryptography/hazmat/primitives/asymmetric/padding.py b/src/cryptography/hazmat/primitives/asymmetric/padding.py
index a37c3f90..828e03bc 100644
--- a/src/cryptography/hazmat/primitives/asymmetric/padding.py
+++ b/src/cryptography/hazmat/primitives/asymmetric/padding.py
@@ -5,7 +5,6 @@
 from __future__ import absolute_import, division, print_function
 
 import abc
-import math
 
 import six
 
@@ -73,7 +72,7 @@ def calculate_max_pss_salt_length(key, hash_algorithm):
     if not isinstance(key, (rsa.RSAPrivateKey, rsa.RSAPublicKey)):
         raise TypeError("key must be an RSA public or private key")
     # bit length - 1 per RFC 3447
-    emlen = int(math.ceil((key.key_size - 1) / 8.0))
+    emlen = (key.key_size + 6) // 8
     salt_length = emlen - hash_algorithm.digest_size - 2
     assert salt_length >= 0
     return salt_length
diff --git a/tests/hazmat/primitives/test_rsa.py b/tests/hazmat/primitives/test_rsa.py
index 9a0aaf1a..e6482651 100644
--- a/tests/hazmat/primitives/test_rsa.py
+++ b/tests/hazmat/primitives/test_rsa.py
@@ -6,7 +6,6 @@ from __future__ import absolute_import, division, print_function
 
 import binascii
 import itertools
-import math
 import os
 
 import pytest
@@ -434,7 +433,7 @@ class TestRSASignature(object):
             ),
             hashes.SHA1()
         )
-        assert len(signature) == math.ceil(private_key.key_size / 8.0)
+        assert len(signature) == (private_key.key_size + 7) // 8
         # PSS signatures contain randomness so we can't do an exact
         # signature check. Instead we'll verify that the signature created
         # successfully verifies.
@@ -1428,7 +1427,7 @@ class TestRSADecryption(object):
             )
         ).private_key(backend)
         ciphertext = binascii.unhexlify(example["encryption"])
-        assert len(ciphertext) == math.ceil(skey.key_size / 8.0)
+        assert len(ciphertext) == (skey.key_size + 7) // 8
         message = skey.decrypt(ciphertext, padding.PKCS1v15())
         assert message == binascii.unhexlify(example["message"])
 
@@ -1684,7 +1683,7 @@ class TestRSAEncryption(object):
         public_key = private_key.public_key()
         ct = public_key.encrypt(pt, pad)
         assert ct != pt
-        assert len(ct) == math.ceil(public_key.key_size / 8.0)
+        assert len(ct) == (public_key.key_size + 7) // 8
         recovered_pt = private_key.decrypt(ct, pad)
         assert recovered_pt == pt
 
@@ -1725,7 +1724,7 @@ class TestRSAEncryption(object):
         public_key = private_key.public_key()
         ct = public_key.encrypt(pt, pad)
         assert ct != pt
-        assert len(ct) == math.ceil(public_key.key_size / 8.0)
+        assert len(ct) == (public_key.key_size + 7) // 8
         recovered_pt = private_key.decrypt(ct, pad)
         assert recovered_pt == pt
 
@@ -1750,7 +1749,7 @@ class TestRSAEncryption(object):
         public_key = private_key.public_key()
         ct = public_key.encrypt(pt, pad)
         assert ct != pt
-        assert len(ct) == math.ceil(public_key.key_size / 8.0)
+        assert len(ct) == (public_key.key_size + 7) // 8
         recovered_pt = private_key.decrypt(ct, pad)
         assert recovered_pt == pt
 
diff --git a/tests/utils.py b/tests/utils.py
index ca3245b0..7e79830b 100644
--- a/tests/utils.py
+++ b/tests/utils.py
@@ -7,7 +7,6 @@ from __future__ import absolute_import, division, print_function
 import binascii
 import collections
 import json
-import math
 import os
 import re
 from contextlib import contextmanager
@@ -744,15 +743,15 @@ def load_x963_vectors(vector_data):
             vector["key_data_length"] = key_data_len
         elif line.startswith("Z"):
             vector["Z"] = line.split("=")[1].strip()
-            assert math.ceil(shared_secret_len / 8) * 2 == len(vector["Z"])
+            assert ((shared_secret_len + 7) // 8) * 2 == len(vector["Z"])
         elif line.startswith("SharedInfo"):
             if shared_info_len != 0:
                 vector["sharedinfo"] = line.split("=")[1].strip()
                 silen = len(vector["sharedinfo"])
-                assert math.ceil(shared_info_len / 8) * 2 == silen
+                assert ((shared_info_len + 7) // 8) * 2 == silen
         elif line.startswith("key_data"):
             vector["key_data"] = line.split("=")[1].strip()
-            assert math.ceil(key_data_len / 8) * 2 == len(vector["key_data"])
+            assert ((key_data_len + 7) // 8) * 2 == len(vector["key_data"])
             vectors.append(vector)
             vector = {}